Modem network communication systems are generally of either the wired or wireless type. Wireless networks enable communications between two or more nodes using any number of different techniques. Wireless networks rely on different technologies to transport information from one place to another. Several examples, include, for example, networks based on radio frequency (RF), infrared, optical, etc. Wired networks may be constructed using any of several existing technologies, including metallic twisted pair, coaxial, optical fiber, etc.
Communications in a wired network typically occurs between two communication transceivers over a length of cable making up the communications channel. Each communications transceiver comprises a transmitter and receiver components. The receiver component typically comprises one or more cancellers. Several examples of the type of cancellers typically implemented in Ethernet transceivers, especially gigabit Ethernet transceivers include, echo cancellers, near-end crosstalk (NEXT) cancellers, far-end crosstalk cancellers (FEXT), etc.
The deployment of faster and faster networks is increasing at an ever quickening pace. Currently, the world is experiencing a vast deployment of gigabit Ethernet (GE) devices. As the number of installed gigabit Ethernet nodes increases, the need for reliable, comprehensive and user-friendly cable diagnostic tools has become more important than ever. The wide variety of cables, topologies and connectors deployed results in the need for non-intrusive identification and reporting of cable faults. It would be desirable to have a system capable of identifying and characterizing noise sources affecting a link and reporting these noise sources in the event the noise source exceeds a permitted envelope, as defined by the relevant standards.
The ability to gather diagnostics on the cable is particularly useful in the case where physical access to the cable is extremely difficult or impossible. Further, it is desirable to have the cable diagnostics capabilities built into the communications transceiver without requiring significant modification to existing transceivers. One of the impairments commonly encountered in Ethernet networks, especially gigabit Ethernet networks, is FEXT noise.
The estimation of the FEXT impairment is typically performed using residual noise measurements made during the regular operating mode of the system. The noise impairment is calculated using a simple energy calculation. The disadvantage of such a measurement, however, is that the measured noise in actuality comprises a combination of several noise sources, such as thermal noise, NEXT noise, FEXT noise and many others. As a result, isolation of the FEXT noise is not possible or at best is inaccurate.
Another prior art approach to estimating the FEXT noise requires stopping the normal operation of the system and transmitting on adjacent interfering cables (i.e. wire pairs) only, and measuring the noise present on the cable or wire pair under test. A disadvantage of such a system is that the system must be stopped from its regular communication tasks. Further, monitoring and processing need to be performed, preferably by a well-trained technician. While this method achieves the goal of measuring the FEXT noise, the measurement procedure is complex and it interferes with the regular operation of the system. Moreover, stopping the normal operation of the system is not always possible.
Thus, there is a need for a mechanism for detecting and estimating the FEXT impairment in a communications system such as a gigabit Ethernet or DSL system that can be incorporated into a conventional communications transceiver that is efficient and is relatively low cost in terms of hardware requirements.